Rapid, Quantitative Nuclear Magnetic Resonance Test for Oxygen-17 Enrichment in Water

Nuclear magnetic resonance (NMR) studies involving ¹⁷O are increasingly important in molecular biology, material science, and other disciplines. A large number of these studies employ H₂¹⁷O as a source of ¹⁷O, and this reliance can be limiting because the high cost of H₂¹⁷O. To overcome this constraint, a recent study proposed a distillation scheme capable of producing significant quantities of H₂¹⁷O at a low cost. Although this method is reported to be effective, the reactions proposed to quantify percent of ¹⁷O enrichment are either time intensive or have a risk of errors due to the isotope effect. Here, an alternative reaction scheme is described to measure ¹⁷O water that ultimately creates methyl benzoate as the sole ¹⁷O-containing product. The proposed reaction is completed in a matter of minutes at room temperature, produces only one ¹⁷O product, and requires no clean-up step. The large isotope shift observed in solution NMR between the ¹³C═¹⁶O and ¹³C═¹⁷O resonances allows for integration of the individual peaks. This ¹³C NMR analysis is found to be highly accurate over a wide enrichment range and is accessible to most NMR spectroscopists.